in the P ollen-Mother-Cells of Larix . 307 
to certain chemical processes, and it does its work by means 
of the energy set free by these or by other chemical processes ; 
but it is also a machine, adapted by its structure to utilize in 
a definite way the energy so liberated. 
The investigations here described were begun at the sugges- 
tion of Professor R. A. Harper, and have been carried on with 
the continued assistance of his direction and criticism. 
Madison, Wisconsin. 
June 17, 1902. 
